As the demand of users for bandwidth is rapidly increasing, optical transmission systems, where subscriber traffic is transmitted using optical networks, is installed to serve this demand. These networks are typically referred to as fiber-to-the-curb (FTTC), fiber-to-the-building (FTTB), fiber-to-the-premise (FTTP), or fiber-to-the-home (FTTH). Each such network provides an access from a central office (CO) to a building, or a home, via optical fibers installed near or up to the subscribers' locations. As the transmission quantity of such an optical cable is much greater than the bandwidth actually required by each subscriber, a passive optical network (PON) shared between a plurality of subscribers through a splitter was developed.
An exemplary diagram of a typical PON 100 is schematically shown in FIG. 1. The PON 100 includes M optical network units (ONUs) 120-1, 120-2, through 120-M, coupled to an optical line terminal (OLT) 130 via a passive optical splitter 140. To the extent that reference is made to the ONUs without regard to a specific one thereof, such ONUs will be referenced as 120. Traffic data transmission may be achieved, for example, by using asynchronous transfer mode (ATM) cells over two optical wavelengths, one for the downstream direction and another for the upstream direction. Other multiplexing methods are available such as Ethernet frames in EPON or data fragments in GPON. Downstream transmission from OLT 130 is broadcast to all ONUs 120. Each ONU 120 filters its respective data according to, for example, pre-assigned ATM VPI/VCI values. The ONUs 120 transmit respective data to the OLT 130 during different time slots allocated by the OLT 130 for each ONU 120. The splitter 140 splits a single line into multiple lines, for example 1 to 32.
In the related art, PONs are classified into one of the following: an ATM PON (APON), a broadband PON (BPON), an Ethernet PON (EPON or GE-PON), and a Gigabit PON (GPON). The APON uses the ATM protocol; the BPON is designed to provide broadband services over an ATM protocol; the EPON accommodates an Ethernet protocol; and the GPON is an evolution of BPON with higher speeds as well as the ability to accommodate various types of information (e.g., ATM, Ethernet, TDM, and so on) natively. Each type of PON is a standard technology.
The OLT 130 and ONUs 120 provide the interface between the optical network and homes or businesses, and thus define the type of the PON. For example, in order to establish a BPON the OLT 130 and ONUs 120 should be compatible with the BPON standards, ITU-T-G.983 series. ONU's components adapted to operate in a dual mode (e.g., BPON and GPON or EPON and GPON) or components that can function in a triple mode (e.g., BPON, GPON and EPON) are currently being developed. In a case where a mixed-mode ONU is utilized, the network type is determined by the OLT installed at the CO and the ONUs detect the mode of the PON supported by the OLT.
To save costs on infrastructure, service providers have installed mixed-mode ONUs in homes or businesses, and thus can upgrade, or provide additional services with minimal or without additional investments. Specifically, to upgrade the network from a first type of PON to a second type of PON, the OLT in the CO is replaced with an OLT that supports the second PON and mixed-mode ONUs are configured to operate in accordance with the second OLT. Presently, each ONU 120 has to be physically replaced, by a technician, when the mode and/or standard implemented on the PON changes. This is of course a time consuming and labor-intensive task that extends the time required for upgrading the network and involves significant costs for service providers. Furthermore, the labor intensive replacement of the ONUs 120 can result in prolonged interruption of services to the subscribers.
It would be, therefore, advantageous to provide a method for automatically upgrading ONUs to operate a new type of PON, and thus allowing the smooth migration between the different types of PON.